Need a new prop :(

[SHickey]

Hello,

I have a 1978 StarCraft American 20 that has a 165 HP Mercruiser motor and a MC-1 outdrive. It weighs 1700 lbs. The prop on it now is an aluminum 15 1/2 x 17 that has a bunch of nicks and gouges on it from old age. I wanted to replace the prop with a stainless steel model and I was wondering if the size and pitch of the prop should be duplicated. I know SS props have far less flex than aluminum ones so I was wondering if the change in prop material required a different size or pitch.

I have a spare 15 1/2 19P aluminum prop that I have tested on the boat before but it seems to take longer to plane out with the 19P so I'm not sure if that would be a good size for a SS prop. The top speed with the 17P is @ 35 mph maybe a little more if I am by myself but I usually cruise @ 10 - 25 MPH due to a wife that does not like to go fast.

Any advice is most welcome and stay safe on the water.

SH

 

[alldodge]

The 19 pitch sure sounds like to much pitch, and I would stick with the 17
The blades are thinner or a stainless prop, but I would stick with the same pitch.
Are you reaching max RPM's at WOT?

 

[SHickey]

Thanks for the response,

The old straight six has an annoying internal tick in the motor so I don,t go much higher than 3500 rpm (and only for short periods of time) if that makes sense. So the consensus is I can buy the same size SS prop as the Aluminum 151/2 X 17P I am already using. I am hoping the SS will give me a little better performance.

Lastly, are the SS props repairable with hand files similar to the aluminum props if they develop small nicks or gouges??

Thanks again

 

[alldodge]

Lastly, are the SS props repairable with hand files similar to the aluminum props if they develop small nicks or gouges??

The stainless props can have the edge filed smooth if there is a nick, but stainless is much harder to do. That said if you hit something with an aluminum prop it bends and breaks easy. If you hit something with a stainless it doesn't bend easy so it has a better chance of breaking something inside the drive

 

[briangcc]

If your existing prop gives you the performance you like, why not have it repaired? Shop here charged me $50 to do so as I had nicks on all 3 blades of mine. Much cheaper than a new prop! As you have a spare, albeit with less performance, the time to repair shouldn't be an issue.

 

[SHickey]

That is a good idea

I didn't really consider repairing the prop because the blade tips are pretty thin from my own nick filing repairs and I would suspect any repair would slightly reduce the present diameter even farther.

I am willing to spend the money on a more durable and better performing prop since I only get to use my boat @ 5 months during the year. I just want to make sure I don't need to compensate for the prop size when switching between Aluminum to SS if that makes sense.

SH

 

[briangcc]

I get it - boating season typically here is 3 months but climate change has pushed that to about 7 months. But you may want to review AllDodge's post. When you strike something the weakest link gives. Right now, that's your AL prop. Switch to a SS prop and your lower unit becomes the weakest link. Which is cheaper to repair/replace - lower unit or prop?

Any prop shop worth it's salt will weld in material if they need to in order to get the blades back to spec. Mine had material added back on all 3 blades - I was avoiding a 10 yr old in a tiller boat who was gunning straight for me, the prop struck bottom trying to avoid him.

 

[Sea Rider]

The old straight six has an annoying internal tick in the motor so I don,t go much higher than 3500 rpm (and only for short periods of time) if that makes sense.
Thanks again

Have you tached current prop at wot as loaded, what was max rpm achieved ? How do you know is thre right prop for your boating needs ? Need to have that OB revving at least middle to max wot rpm range factory stated.

Happy Boating